This invention relates to an inside diameter machining method suitable for turning machining in order to form a machining hole, such as a bag hole having the entrance of a hole smaller than the machining diameter of its inside.
In this kind of bag hole machining in a conventional way, a cutting tool for boring fitting to the machining diameter of the inside can not be inserted into the inside of a workpiece since the entrance of a hole is smaller than the machining diameter of the inside. Then, the machining with the cutting tool for boring is impossible. So, the machining is performed in such a state that the formed tool formed in the shape to be machined in advance is set in a workpiece.
But, since in such a way it is necessary to prepare a specific formed tool, this way can not be used for general purposes. Besides, complex arrangement, such as setting a formed tool in a workpiece, is necessary, and efficient machining is impossible.
In addition, it is difficult to improve the machining accuracy in the machining with a formed tool.
The object of the present invention is to provide inside diameter machining method capable of performing bag hole machining using a normal cutting tool, such as a cutting tool for boring, without using formed tool, taking the above-mentioned circumstances into consideration.
The invention of claim 1 is inside diameter machining method in boring machining for machining inside a workpiece using a turning tool having cutting portion at an end portion of its main body in the shape of a bar, comprising:
at the time of turning machining on the machining hole where the size of a tool insertion hole of the workpiece into which the turning tool (for instance, the diameter D2, is not always a circular hole) is inserted is smaller than the machining diameter of the portion to be machined inside the workpiece,
moving said turning tool in a first axial direction and in a second axial direction orthogonal to each other (for instance, the X-axis direction and the Z-axis direction) and in a rotational direction (for instance, the B-axis direction) with a third axial direction orthogonal to both first and second axial directions (for instance, the Y-axis direction) as its center from said tool insertion hole of a workpiece to be machined along tool shape of said turning tool so as to position cutting portion of said turning tool at the portion to be machined inside the workpiece; and
starting turning machining on the portion to be machined of said workpiece in the above-mentioned state.
In the invention of claim 1, by moving the turning tool in the rotational direction (for instance, the B-axis direction) with the third axial direction (for instance, the Y-axis direction) as its center, the cutting portion of the turning tool can be positioned at the portion to be machined of the inside of the workpiece with no interference between the turning tool and the workpiece. Then, the machining for forming machining hole, such as a bag hole, is possible without using a formed tool as a turning tool.
In the invention of claim 2, turning tool is held by turning tool holding means provided with a spindle side for rotating and driving said workpiece at the time of machining of the inside of said workpiece so as to prevent chatter of the turning tool.
According to the invention of claim 2, accurate inside diameter machining is possible since the chatter of the cutting tool can be effectively prevented by the cutting tool holding means.
In the invention of claim 3, firstly, the top end portion of said turning tool is inserted into said tool insertion hole, subsequently the main body portion of the turning tool continuing to the top end portion is inserted, and furthermore the main body portion of the turning tool continuing to the inserted main body portion is inserted when the turning tool is inserted into said workpiece.
According to the invention of claim 3, the turning tool is gradually inserted into the tool insertion hole along the whole length of the tool body, starting the top end portion thereof. Then, the turning tool can pass through the tool insertion hole of the workpiece, making use of the portion which section is the smallest, and the occurrence of the interference between the workpiece and the turning tool can be effectively prevented.